This invention relates to carburetors, and more particularly to an air-fuel mixture enrichment circuit that facilitates engine starting.
Most engines require a mixture enrichment system to improve or even allow starting. An enrichment system is especially necessary when the engine is cold, or after the engine has been run out of fuel. The two common means of enrichment in the field of small engines are the choke and the primer.
The choke provides enrichment by closing off the front end of the air intake of a carburetor to allow a manifold vacuum to draw on all of the fuel passages that open to the air intake. The disadvantage of the choke is that the user must close the choke completely and then crank the engine until they hear a false start. The choke is then partially opened and the engine is cranked until it starts. When the engine is warmed up 30 to 40 seconds, the choke is opened fully. This operation is too complex for many users and results in many field returns and complaints.
The primer uses a manually operated bulb to inject fuel into the carburetor throat. The disadvantage of the primer is that a simple primer cannot regulate the amount of fuel injected into the carburetor throat which makes it easy for the user to over- or under-prime the engine, resulting in no start.
An improved enrichment system uses an auxiliary fuel pump coupled with the carburetor body. The auxiliary fuel pump provides enrichment by injecting fuel into the carburetor throat when starting the engine. To prevent over- or under-priming the engine, the auxiliary fuel pump uses a pulse emitted from the engine""s crankcase to control the fuel injection. This approach is described in more detail in U.S. Pat. No. 5,706,774, entitled xe2x80x9cCarburetor Start Pump Circuit,xe2x80x9d filed on May 24, 1996, which is hereby incorporated by reference in its entirety.
When using a system such as the auxiliary fuel pump described above, it may be desirable to deactivate the system when the engine warms up because a constant fuel-air ratio will have been obtained, and thus, there would be no need for additional fuel injection. However, often times, the user may forget to do so or may engage the system when the engine is already running and is warmed up or hot. This may result in the engine xe2x80x9cconking outxe2x80x9d or stalling due to too much fuel being injected into the carburetor throat while the engine is running.
Therefore, it is believed that an improved carburetor start pump circuit would be desirable.
The carburetor start pump circuit of the present invention serves to facilitate engine starting in a simple manner that is independent of manifold vacuums and capable of regulating the amount of fuel injected into the carburetor throat to ensure the engine is properly primed. It preferably has an auxiliary fuel pump mounted on a relatively standard carburetor body, a start pulse passage extending through the carburetor body to the auxiliary fuel pump, and a fuel circuit having an intake side which extends from a metering chamber of the carburetor body to the auxiliary fuel pump and a discharge side which is interconnected to the intake side and extends from the auxiliary fuel pump to a throttle bore in the air intake of the carburetor body. To prevent the engine from stalling, a restriction jet is placed within the start pulse passage to limit the amount of fuel that the auxiliary pump may discharge into the throttling bore when the engine transmits pulses at high frequencies.
An object of this invention is to provide an improved carburetor start pump circuit.
Further, objects and advantages of the invention will become apparent from the following detailed description and accompanying drawings.